1. Field of the Invention
The present invention relates to a segment type color wheel suitable as a filter element of a time-share light dispersing device, and to a manufacturing method of the same.
2. Description of the Related Art
Color composition in a projection-type image display apparatus has conventionally been accomplished commonly by a method, such as: a single-panel method, in which one light valve element adapted to control light amount per pixel thereby creating an image is used to disperse each pixel into red (R), green (G), and blue (B) lights; and a three-panel method, in which three light valve elements dedicated to R, G and B lights, respectively, are used to produce R, G and B images in parallel, and then the three images thus produced are combined. Currently, as a light valve element capable of fast switching, such as a ferroelectric liquid crystal display element or a digital micro mirror device, is increasingly coming into practical use, a time-sharing single-panel method is widely used. In the time-sharing single-panel method, R, G and B lights are caused to sequentially impinge on one light valve element, the light valve element is driven in synchronization with switching-over of the R, G and B lights thereby producing R, G and B images in a time-series manner, and the images thus produced are projected onto a screen, or the like. Here, color composition of the images is accomplished by a viewer due to an afterimage effect occurring at a sense of vision. In the time-sharing single-panel method, reduction in both dimension and weight of the apparatus, which is a feature of a single-panel method, can be achieved by employing a relatively simple optical system, and therefore the time-sharing single-panel method is favorable for realizing inexpensive fabrication of a projection-type image display apparatus. In such an image display apparatus, a color wheel is preferably used as a filter element of a time-share light dispersing device to sequentially disperse light emitted from a white light source into R, G and B lights having respective wavelength bands in a time-sharing manner.
FIGS. 6A and 6B are respectively top plan and side views of a conventional and typical color wheel assembly 200 as a time-share light dispersing device including such a color wheel as described above. Referring to FIG. 6B, the color wheel assembly 200 includes a color wheel 100, and a driving motor 106 including a motor hub 105. The color wheel 100 is a tricolor color wheel composed of a disk-like substrate 101 which is made of a light-transmitting material, for example, optical glass, and three pie-shaped (sectorial) filters 102, 103 and 104 which are formed on a surface of the substrate 101, and which exclusively transmit, for example, R, G and B lights, respectively. The color wheel 100 thus structured is fixedly attached to the motor hub 105 coaxially therewith. The color wheel assembly 200 operates such that the color wheel 100 is spun by the driving motor 106 so that white light S impinges sequentially on the filters (R, G and B) 102, 103 and 104 whereby the white light S is sequentially dispersed into R, G and B lights.
FIGS. 7 and 8 are respectively top plan and exploded side sectional views of a segment type color wheel 160, which is structured such that a plurality (four in FIG. 7) of pie-shaped color filter segments 112, 114, 116 and 118 separately prepared are fixed in position by means of a support member 120 and a clamp member 122 so as to form a disk.
Specifically, as shown in FIG. 8, inner circumferences 112a, 114a, 116a and 118a of the color filter segments 112, 114, 116 and 118 are fitted to an outer circumference of a smaller cylinder portion 120a of the support member 120 whereby the color filter segments 112, 114, 116 and 118 are duly set in position in the radial direction of the color wheel 160, and surfaces thereof located toward the inner circumferences 112a, 114a, 116a and 118a are fitted to an annular seat portion 120b of the support member 120 whereby the color filter segments 112, 114, 116 and 118 are duly set in position in the thickness direction of the color wheel 160. Then, a smaller cylinder portion 122a of the clamp member 122 is engagingly inserted into a hollow 120c of the support member 120 so that an annular seat portion 122b of the clamp member 122 and the aforementioned annular seat portion 120b of the support member 120 sandwich and clamp the inner circumferential portions of the color filter segments 112, 114, 116 and 118. And, when the support member 120 and the clamp member 122 are bonded or screwed together, the color filter segments 112, 114, 116 and 118 are fixed as one piece structure. The color wheel 160 thus structured is fixedly attached to a hub (such as the hub 105 as shown in FIGS. 6A and 6B) of a motor (such as the driving motor 106 as shown FIG. 6B) such that the hub is inserted in the hollow 122c of the clamp member 122 constituting the color wheel 160 (refer to, for example, paragraph [0010] and FIG. 6 in Japanese Patent Application Laid-Open No. 2004-101827, and claim 1 and FIG. 2 of Japanese Patent Application Laid-Open No. H10-48542).
FIG. 9 is a top plan view of another segment type color wheel 124 including color filter segments 126, 128, 130 and 132. The color filter segments 126, 128, 130 and 132 have respective inner circumferences 126a, 128a, 130a and 132a, which are not subjected to optical characteristic constraints, and which are formed straight as shown in the figure (or alternatively circular with a small curvature), whereby the workability is improved enabling cost reduction in production. Recently, cost reduction by such a method is increasingly requested along with downsizing of a color wheel. The color filter segments 126, 128, 130 and 132 further have respective outer circumferences 126b, 128b, 130b and 132b, and both sides 126c/126d, 128c/128d, 130c/130d and 132c/132d which meet respectively with the outer circumferences 126b, 128b, 130b and 132b at a right angle, and which meet respectively with the inner circumferences 126a, 128a, 130a and 132a at an angle greater than 90 degrees.
When a color filter segment is carved out of a glass substrate scribed by a scriber, burrs may be unwantedly formed. Referring to FIG. 10A showing an enlarged view of a part of the color filter segment 130, indicated by A in FIG. 9, and also to FIG. 10B showing a cross sectional view of the color filter segment 130, taken along line B-B in FIG. 10A, a burr 134 is formed at the side 130c of the color filter segment 130. The burr 134 thus formed has a dimension H normally measuring several hundreds of micron meters, and causes a gap (spoke) to be formed between the side 130c of the color filter segment 130 and the side 132d of the color filter segment 132, which, in the worst case, prohibits assembly of the color wheel 124. Since the increase of the spoke width generally causes the light utilization to lower, the color purity to deteriorate, and the wind noise to increase, the spoke dimension needs to be minimized.
It is verified by the present inventors et al. that, for example in case of the color filter segment 130, such a burr is often formed at innermost end portions of the sides 130c and 130d intersecting with the inner circumference 130a at an angle larger than 90 degrees, and therefore the processes of inspecting and removing burrs are definitely required, which inevitably increases the number of manufacturing processes thus pushing up production cost.